Problem with GSSAPI

[Luca Bertoncello]

Hi list!

I'm really puzzled...
I have a Mailserver with Dovecot 2.2.9 (installed from Ubuntu
14.04-Repositories) and it works well with LDAP-Authentication agains the
Active Directory.

Now I want to use GSSAPI to allow the clients (with Thunderbird 38.7.1) to
read E-Mails without giving a password.

I configured Dovecot using these HowTos:

http://mindref.blogspot.de/2011/02/dovecot-kerberos.html
http://wiki.dovecot.org/Authentication/Kerberos

But it does not work...
In mail.log I can just see:

Apr  3 09:52:26 mail dovecot: auth: Debug: Loading modules from directory: /usr/lib/dovecot/modules/auth
Apr  3 09:52:26 mail dovecot: auth: Debug: Loading modules from directory: /usr/lib/dovecot/modules/auth
Apr  3 09:52:26 mail dovecot: auth: Debug: Module loaded: /usr/lib/dovecot/modules/auth/libmech_gssapi.so
Apr  3 09:52:26 mail dovecot: auth: Debug: Loading modules from directory: /usr/lib/dovecot/modules/auth
Apr  3 09:52:26 mail dovecot: auth: Debug: Module loaded: /usr/lib/dovecot/modules/auth/libauthdb_ldap.so
Apr  3 09:52:26 mail dovecot: auth: Debug: Read auth token secret from /var/run/dovecot/auth-token-secret.dat
Apr  3 09:52:26 mail dovecot: auth: Debug: auth client connected (pid=2300)
Apr  3 09:52:26 mail dovecot: imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=192.168.50.54, lip=192.168.50.3, session=<x8Sq5I8vsADAqDI2>

and Thunderbird says that the Ticket was not accepted and I have to check
if I'm logged into the Kerberos/GSSAPI subsystem.
I checked with tcpdump and I see that Thunderbird does NOT send at all any
request.

Could someone help me?

Thanks a lot!
Luca Bertoncello
(lucabert at lucabert.de)